Chemical dehumidifiers wherein a liquid desiccant, for example an aqueous glycol solution or a solution of lithium chloride or lithium bromide in water is used to remove moisture vapor from air being conditioned have long been available. Although chemical dehumidifiers of the indicated type are advantageous in operations of many types, their comparatively high energy requirements, particularly for regeneration of the liquid desiccant, have rather severely restricted their use. Furthermore, when the desiccant solution is heated to cause vaporization of water therefrom and consequent regeneration, the consequence is hot, concentrated hygroscopic solution. Since the ultimate use in dehumidification requires the hygroscopic solution to be at a comparatively low temperature, energy is also required to transfer heat from the regenerated solution.
Thermal compressors, wherein water is vaporized at a low pressure and at a comparatively low temperature from a thin film flowing along a thin separating member, and is condensed at a slightly higher temperature and pressure on the opposite side of the separating member are known*. Concentrated salt solution and condensed water are separately collected. Thermal compressors have been suggested for use in releasing fresh water from sea water and other brine sources, so that the concentrated salt solution has ordinarily been discarded, or used as a feedstock for a salt recovery process, while the condensed water has been the desired end product. FNT *See, for example, U.S. Pat. No. 2,734,023 and "Sea Water Converter: Metal Sheet Evaporates Water and Condenses Vapor", Machine Design